The invention pertains generally to coal liquefaction and particularly to coal liquefaction by oxidation and heating.
Chemically, coal is a compacted mixture of organic compounds containing carbon, hydrogen, nitrogen, sulfur and oxygen. A very high proportion of the compounds comprises large aromatic molecules, i.e., molecules having a molecular weight of at least 1000.
In order to obtain usable liquid hydrocarbons or oil-soluble solids, the large molecules must be broken into molecules with a molecular weight of no more than 400. Saturation of the molecule also increases the liquefaction of the coal. A widely used technique for cracking coal molecules is pyrolysis which proceeds by breaking C--C bonds with thermal energy. The disadvantages of this method are the requirement of a coal particle size from 75 to 150 microns, an absence of oxygen during the process, high temperatures and long heating times, and low yields. A more successful technique is hydrogenation which proceeds by saturating unsaturated bonds and hydrogenating C--C bonds broken by catalysis, heat, and pressure. The disadvantages of this method are that it requires moderately high temperatures, high hydrogen pressures, a small particle size from 75 to 150 microns, and expensive processing equipment. The yield is much better than yields from pyrolytic methods. The amount of usable products can be as high as 50 to 55 percent of the original weight of coal.